GATE 2025 BT – Question 57
A binary mixture of benzene and toluene under vapour-liquid equilibrium at 80 $^o$C follows ideal Raoult's law. At this condition, the saturation pressures of benzene and toluene are 101 kPa and 40 kPa, respectively. If the mole fraction of benzene in the liquid phase is 0.6, the corresponding mole fraction of benzene in the vapour phase will be _______. (Round off to two decimal places)
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Correct answer: 0.78 to 0.80
Explanation
By Raoult's law the partial pressure of benzene is $0.6 \times 101 = 60.6$ kPa and that of toluene is $0.4 \times 40 = 16$ kPa. The vapour fraction of benzene is $y = \frac{60.6}{60.6 + 16} = 0.79$.